What are the disadvantages and overheads of a single-ton class?

Hello, I am a beginner developer who is developing games with C++ and DirectX.

My question is that not only games but also various design patterns are applied when developing software Among them, Singleton has the advantage of easily accessing any source file instead of global variables I don't think there's much disadvantage as I use it comfortably.

The disadvantage that I know is that you have to use it when there is only one instance. The part that I apply to the actual game is SceneManager or BulletManager (which is used in many other places) and I usually use it as an object called 'Manager'? There seems to be no problem as long as it is used as one instance.

In any source file, GetInstance is defined as a macro without an exit and is easily accessed I think that the overhead that occurs at this time is more common sense than it exists as a class member variable. However, if the overhead is insignificant, I will continue to use it, but since the life of the game is FPS, I don't think even this can be ignored.

Anyway, what are the disadvantages of using a single tone pattern? Also, do you have enough overhead to care about? Is single tone used a lot in game development and software development?